The present application relates to an electrode with the superior contact characteristics between the current collector and the active material layer and a battery including the electrode.
In recent years, portable electronic devices such as combination cameras (videotape recorder), mobile phones, and portable computers have been sophisticated and multi-functionalized. Accordingly, a higher capacity of a secondary battery as a power source for these mobile devices has been demanded. Currently, a lithium ion secondary battery using graphite for the anode is generally used. However, since the technique has been matured in such a lithium ion secondary battery, the battery capacity thereof is in a saturated state and thus it is difficult to attain a vastly high capacity thereof. Therefore, it is considered to use silicon for the anode. In recent years, it has been reported that an anode active material layer is formed on an anode current collector by vapor-phase deposition method or the like. Silicon is largely expanded and shrunk due to charge and discharge, and thus it has been an issue that the cycle characteristics are lowered due to pulverization. However, by using vapor-phase deposition method, pulverization can be prevented, and the anode current collector and the anode active material layer can be integrated. In the result, electron conductivity in the anode becomes extremely favorable, and high performance both in the capacity and in the cycle life is expected.
However, even in the anode in which the anode current collector and the anode active material layer are integrated as above, the following issue exists. That is, when charge and discharge are repeated, the anode active material layer is intensely expanded and shrunk, and thus a stress is applied between the anode current collector and the anode active material layer. In the result, for example, the anode active material layer is dropped, and the cycle characteristics are lowered. Therefore, it has been already considered that by roughening the surface of the anode current collector, the contact characteristics between the anode active material layer and the anode current collector are improved (for example, refer to International Publication No. WO01/031723 and Japanese Unexamined Patent Application Publication No. 2002-313319).
However, when the surface roughness of the anode current collector is excessively increased to improve the contact characteristics between the anode active material layer and the anode current collector, the impedance is increased in the interface with an electrode lead (tab) provided in part of the surface of the anode current collector. In the result, the cycle characteristics may be deteriorated.